Preferably, a vehicular suspension for use in an automobile or the like has progressive spring characteristics in relation to bounds of a wheel. Conventionally, suspensions having such progressive spring characteristics have been proposed in various configurations. For example, Japanese Utility Model Application Laid-Open (kokai) No. H7-11403 describes a suspension shock absorber for imparting, to a suspension, progressive spring characteristics in relation to bound strokes from a neutral position of a wheel.
Like a suspension equipped with the above-mentioned suspension shock absorber, a conventional suspension which has progressive spring characteristics in relation to bound strokes of a wheel includes a plurality of springs of different fixed spring constants and functions such that the springs generate spring forces in different respective regions of a bound stroke of a wheel. Accordingly, the relation of spring forces to a bound stroke of a wheel is a discontinuously nonlinear relation; in other words, the relation fails to exhibit preferred continuous nonlinearity.
Also, the conventional suspension having progressive spring characteristics exhibits progressive spring characteristics in relation to bound strokes of a wheel, but fails to exhibit progressive spring characteristics in relation to rebound strokes of a wheel. Generally, rebounds of a wheel are restrained by means of a rebound stopper. Accordingly, when a wheel rebounds with a high stroke velocity, the rebound of the wheel is abruptly restrained by the rebound stopper, so that generation of shock is unavoidable.
Furthermore, in the conventional suspension, vertical motions of a wheel associated with bounds and rebounds of the wheel are transmitted to a suspension spring via a link mechanism which includes suspension members, such as a suspension arm, thereby elastically deforming the suspension spring. Thus, elastic deformation of the suspension spring is subjected to restrictions associated with motion transmission via the link mechanism; consequently, spring force characteristics in relation to bound and rebound strokes of a wheel are subjected to restrictions associated with motion transmission via the link mechanism.